Abstract: When a laser beam irradiates a cylinder shell, the irradiated area becomes softer and will destroy cylinder shell. On the basis of early work, 3-D solid element is adopted to simulate the stress of internally pressured cylinder shell irradiated by laser. The properties of material varying with temperature are also taken into account in the computation. It is analyzed by numerical simulation that the ratio of circumferential stress and strength of outer shell along axis is affected by irradiation time, laser beam spot radius and power . With the computations, it concludes that the crack will initiate from the beam spot edge at the conditions of short heating time and large inner pressure, the smaller beam spot will easily crack at the condition of the same laser power, and that the ratio of